August 2024 – Center for Invasive Species Prevention

Phytophthoras – unsettling recent developments

tanoak killed by *P. ramorum*; photo by F.T. Campbell

I am belatedly catching up on the situation with regard to Phytophthora ramorum – sudden oak death – in the US and other countries.

For a general factsheet on this plant disease, see profile here. Here, I’m summarizing more detailed information contained in the February, May, and August 2024 newsletters of the California Oak Mortality Task Force (COMTF) (Newsletters for earlier months are posted here.)

To obtain the most recent information, you can attend the Fall 2024 virtual meeting of the Task Force on Tuesday, October 29, 2024, from 1 pm to 3 pm PDT. Speakers will focus on the status of P. ramorum in California and Oregon wildlands.

On the next day, Wednesday, October 30, the Phytophthoras in Native Habitats Work Group will discuss “Threats to California Native Plants” including from viruses and excessive heat, along with other concerns.

Participation is free, but registration is required. Complete agendas and more information will be available soon here. Sessions will be recorded and posted to the same site. Questions? Contact Janice Alexander.

More in-depth information à Matteo Garbelotto’s UC Berkeley class, “Ecology and Impacts of Emergent Forest Diseases in California,” is now available free and online. Recommended reading, lecture recordings, slides, even essay topic suggestions are posted. Subjects covered include several high impact forest diseases, molecular diagnostics, disease control, and prevention.

I note that the recent detections of new outbreaks in forests and nurseries support the importance of weather in promoting or hindering establishment and spread of Phytophthora ramorum.

Phytophthora ramorum in North American Forests

In Oregon, P. ramorum continued to spread in 2023 and the first half of 2024.

These outbreaks were detected through extensive surveillance. Aerial monitoring (in cooperation with the USDA Forest Service) and high-resolution imagery covered more than half a million acres in Curry County — the region between the California border and the Coos County line. Ground surveys covered 860 acres. Sampling included 518 trees; 117 tested were positive for the fungus. Stream baits were deployed to 63 sites; 26 tested positive at least once (COMTF newsletter, February 2024; includes maps).

By summer 2024, 23 new P. ramorum infestations had been detected at or beyond the Generally Infested Area (GIA; the area where the pathogen is most commonly found) since 2021. Some of these involve one of the newly detected clonal lineages. Oregon officials are expecting to expand the state’s quarantine area to 901 square miles – 45% of Curry County. The designated GIA would also be enlarged to 178 square miles(COMTF newsletter, August 2024; contains maps).

Oregon continues trying to treat high-priority infestations. In 2023, the state treated 165 acres infested by one of the newly detected clonal lineages, NA2, in the Humbug Mountain area and 347 acres in the Port Orford infestation. Since 2001, Oregon’s Department of Forestry has completed eradication treatments on more than 9,000 acres at an estimated cost of over $37 million. Federal lands comprised 28% of treated acres; the remainder were private and state lands. Still, more than 1,000 high-priority acres have not been treated because neither state nor federal agencies could provide sufficient funds (COMTF newsletter, February 2024).

The stream baiting program in 64 stream drainages has – so far – detected six positive streams. Ground surveys are planned for the new positive drainages along the north bank of the Rogue River and a stream that drains into the Elk River east of Port Orford (COMTF newsletter, August 2024).

In California, recent wet winters have prompted several new detections. The first was in Del Norte County near previously detected sites. The UC Berkeley-coordinated “SOD Blitz” plans intensive surveys in this region in coming months (COMTF newsletter May 2024; contains map).

Somewhat later, new infestations were detected farther south, in Humboldt Redwoods State Park. The new sites were outside the formerly detected sites, on the north side of the creek and up to the top of the ridge (COMTF newsletter, August 2024).

Scientists have realized another concern: several other pathogens cause symptoms on bay laurel, tanoak, and madrone that are almost indistinguishable from SOD. This development will complicate monitoring (COMTF newsletter for August 2024; see below for more details).

Meanwhile, scientists determined that sites where the P. ramorum epidemic is driven by higher bay laurel (Umbellularia californica) densities sustained a higher genotypic diversity of P. ramorum. While tanoak (Notholithocarpus densiflorus) doesn’t contribute much to infection of true oaks (Quercus spp.) it can infect bay laurel, thus perpetuating the infection. Infected oaks and tanoaks maintain host-specific pathogen genotypes (Kozanitas et al. 2024)

The USDA Forest Service program that monitors streams in the East to detect P. ramorum placed baits in 63 streams in 10 eastern states: Alabama, Florida, Georgia, Illinois, Maryland, Mississippi, North Carolina, Pennsylvania, South Carolina, and Texas. In 2023, positive findings for P. ramorum were detected from two streams in Alabama, and one each in Mississippi and North Carolina. All sites are associated with nurseries that had previously tested positive for P. ramorum. Over the last five years – since 2019 – eight streams in four states have tested positive at least once: five in Alabama, and one each in Mississippi, North Carolina, and South Carolina. The detection in South Carolina is new. Vegetation in the watershed has been sampled multiple times; all samples collected so far — plant, soil, and run-off water – have been negative. The pathogen belongs to the NA1 lineage – the one established in forests in West Coast states. [COMTF newsletter February 2024]

Situation in Europe

The February 2024, the COMTF newsletter summarized the situation in Great Britain. In England, aerial surveillance covered more than 31,000 ha of larch (Larix kaempferi)plantations. Follow-up investigations detected considerably fewer infested sites than the approximately 200 detected in 2022. Most remain in the southwest and northwest of the country. Weather conditions in 2023 were less conducive for sporulation in 2021 and 2022, which seemed to lead to a reduced level of disease in 2022 and 2023.

In Scotland, widespread aerial and ground surveillance detected a number of sites similar to those found since 2018. Scottish authorities note that where positive findings are not quickly followed by tree removal, localized spread occurred.

In Wales, four helicopter surveillance flights identified around 150 sites deserving further investigation. About 60 of these sites held infected trees, mainly larch, but some noble fir (Abies procera). The COMTF newsletter contains a map showing infested locations. This year’s infection level might be less than in previous years, but this might reflect the fact that the infections are in smaller forest blocks. However, the wet and mild weather in autumn/winter 2023 provided optimal conditions for sporulation, so the scientist expected higher infection rates in 2024. The Welsh Government is working on a new strategy for managing P. ramorum.

In Northern Ireland, P. ramorum was described as still active and spreading. Only two surveys were flown. They identified 49 locations for follow-up, many in forests where the pathogen had been found previously. At two locations, follow-up inspections and sampling of larch confirmed infection by a different pathogen, Phytophthora pseudosyringae. So in 2024, larch samples will be tested for both P. ramorum and P. pseudosyringae.

Other Phytopthoras in Europe

English scientists are trying to determine how damaging P. pseudosyringae is on larch. Infections have been observed at several locations in the north of England, as well as in Northern Ireland (COMTF newsletter February 2024).

Mullet et al. (2024) report that P. pseudosyringae is a self-fertile pathogen of woody plants, especially tree species in the genera Fagus, Notholithocarpus, Nothofagus and Quercus. It is found across Europe and in parts of North America and Chile. Genetic studies show that the North American population originated from Europe. P. pseudosyringae can infect roots; the stem collar region; bark; twigs and stems; as well as leaves. They report it is causing particular damage in Great Britain and western North America. Mullet et al. call for investigation of differences in life history traits between the two main population clusters, including their virulence and host ranges.

*Nothofagus obliqua*; photo by Line1 via Wikimedia

Chile (COMTF newsletter May 2024)

Concerned about decades of mortality of Nothofagus trees in native forests in Chile, González et al. 2024 sought to understand which other native plants might be reservoirs of inoculum of the pathogen Phytophthora pseudosyringae — which is a documented causal agent of partial defoliation and bleeding cankers on two native tree species, Nothofagus obliqua and N. alpina. P. pseudosyringae can sporulate on lesions on Cryptocarya alba, Nothofagus dombeyi and N. obliqua leaves. On Sophora macrocarpa, sporulation occurs on both asymptomatic tissues and on lesions. S. macrocarpa is a common understory species in Nothofagus forests, so it might be an inoculum reservoir for epidemic events in them.

Look-alikes on California Bay Laurel (COMTF newsletter May 2024)

Similar symptoms from a wide variety of pathogenic organisms were detected on bay laurels after last year’s wet winter. Among the pathogens — the list is not exhaustive — includes P. cinnamomi, Neofusicoccum nonquaesitum, Ganoderma brownie, P. pseudosyringae, P. nemorosa, Botryosphaeria dothidea, Armillaria gallica, Diplodia corticola, and others.

Foliar symptoms tend to look identical on bay laurel leaves. Two foliar pathogens cause particular concern. The first is an “anthracnose” disease of bay laurel caused by a species of Kabatiella. Although known to be present for ~80 years, this organism did not seem to cause problems until 2023. In multiple locations around the San Francisco Bay area, it has caused extensive browning defoliation of bay laurel crowns. Whether the trees will die is uncertain.

The second focus is on a recently named species, Calonectria californiensis. This organism produces P. ramorum-like similar symptoms on a wide variety of native plants, including bay laurel, tanoak, salal, mock-orange, Oregon-grape, and rhododendron. On most of these plants this fungus causes black spots that can grow to kill entire leaves, but apparently C. californiensis is not a pathogen of woody plant parts. Initial symptoms of infection on bay laurel appear identical to those caused by the SOD pathogen (Phytopthora ramorum). C. californiensis does not appear (yet) to lead to lasting debilitating disease or tree mortality.

Nurseries and Managed Landscapes

In administering APHIS’ cooperative program aimed at minimizing spread of P. ramorum via interstate trade in plants, California’s Department of Agriculture (CDFA) relies – at least in part – on funds from USDA. CDFA received $1,308,771 from APHIS in 2023. More than 300 establishments in California are regulated under the program. They submitted ~ 7,400 P. ramorum regulatory samples to the CDFA in 2023. Seventy-eight of the samples were positive (COMTF newsletter February 2024).

At the end of 2023, seven California nurseries that had tested positive for the presence of P. ramorum were operating under the APHIS regulation governing positive nurseries. This was an increase over previous years; zero in 2022, three in 2021 (COMTF newsletter February 2024 Table 4). During 2024 five nurseries were confirmed as positive. Three of these had tested positive in previous years. Two retail nurseries were newly positive; one of these was apparently infected when it brought in plants from another nursery (COMTF newsletter August 2024). I wonder whether the very wet winters California has experienced lately have enhanced the pathogen’s ability to grow – and be detected.

In Oregon, in 2023 the Department of Agriculture regulated five interstate shippers under federal compliance agreements and a sixth intrastate shipper regulated under state requirements (COMTF newsletter February 2024). Spring compliance surveys tested 1,228 foliar samples; ten were positive. After this nursery incinerated all nearby plants, none of the 1,664 foliar samples tested in the fall was positive.

In 2023, the Washington State Department of Agriculture processed more than 300 plant, soil, and water samples; all were negative. Washington also inspected five of the nine nurseries that had ‘opted-out’ of the Federal program so they can no longer ship interstate. Host material appeared free of symptoms so no samples were collected (COMTF newsletter February 2024).

Washington nurseries and regulators frequently encounter the problem of infected plants being shipped into the state from outside. (P. ramorum has been found in 33 Washington nurseries since 2003.) During 2023, the Washington State Department of Agriculture conducted three trace-forward investigations. Fortunately no infestations were detected (COMTF newsletter February 2024). In March 2024, Washington faced another trace-forward involving plants sold to homeowners (COMTF newsletter May 2024). Thirteen tissue samples and two soil samples all tested negative (COMTF newsletter August 2024)

Finally, Washington conducted stream baiting. In 2023, none of the 66 samples was positive (COMTF newsletter February 2024)

Infested Plants

Most of the plant species on which P. ramorum was detected during these years are the usual ones: Rhododendron, Viburnum, Pieris, Arbutus, Prunus, Camellia, Loropetalum. I think the several Cornus species might be somewhat unusual. Disease was confirmed on a new Cornus species, C. capitata (evergreen dogwood). One taxon — Arbutus x ‘Marina’ — is not yet listed by APHIS as a host because Koch’s postulates have not been completed (COMTF newsletters for February 2024 and August 2024).

Research (summarized in the February 2024 newsletter)

Two studies found evidence of seasonal and weather factors influenced establishment of P. ramorum. One study found a clear seasonal pattern of pathogen incidence in the western US, plus a link to the El Niño-Southern Oscillation (ENSO) (Xuechung et al. 2024. The second study looked at a Japanese larch plantation in Scotland (Dun et al. 2024).

In both Scotland (above) and France (Beltran et al. 2024 2024), scientists demonstrated that prompt action helps to suppress P. ramorum establishment.

APHIS Updates its Regulations

In March 2024, APHIS revised the P. ramorum “Domestic Regulatory Program Manual.” The agency said it updated figures and definitions, clarified operational steps, and revised the Retail Nursery Dealer Protocol (COMTF newsletter for May 2024).

Funding

In Fiscal Year 2024, under the Plant Protection Act Section 7721 program, APHIS funded $1 million worth of projects focused on P. ramorum and related species. This was out of a total $62 million in funds dispersed for pest survey, research, mitigation, and outreach programs. This money funded nursery surveys in 11 states. Also, it paid for a project to evaluate the threat of the NA2 & EU2 lineages to nurseries and forests (COMTF newsletter May 2024).

SOURCES

Beltran, A.; Laubray, S.; Ioos, R.; Husson, C.; Marçais, B. 2024. Low persistence of Phytophthora ramorum in western France after implementation of eradication measures. Annals of Forest Science. 81: 7. https://doi.org/10.1186/s13595-024-01222-1

Dun, H.F.; MacKay, J.J. & Green, S. 2024. Expansion of natural infection of Japanese larch by Phytophthora ramorum shows trends associated with seasonality & climate. Plant Pathology. 73(2): 419-430).

González, M.P.; Mizubuti, E.S.G.; Gonzalez, G.; Sanfuentes, E. 2024. Uncovering the hidden hosts: Identifying inoculum reservoirs for Phytophthora pseudosyringae in Nothofagus forests in Chile. Plant Pathology. 73(4): 937-947. https://doi.org/10.1111/ppa.13855. (Summarized in COMTF newsletter February 2024.)

Kozanitas, M.; Knaus, B.J.; Tabima, J.F.; Grünwald, N.J.; Garbelotto, M. 2024. Climatic variability, spatial heterogeneity & the presence of multiple hosts drive the population structure of the pathogen P ram & the epidemiology of Sudden Oak Death. Ecogeography. https://doi.org/10.1111/ecog.07012. (Summarized in COMTF newsletter May 2024.)

Mullet, M.S.; Harris, A.R.; Scanu, B. [and others]. 2024. Phylogeography, origin & population structure of the self-fertile emerging plant pathogen Phytophthora pseudosyringae. Molecular Plant Pathology. https://doi.org/10.1111/mpp.13450. (Summarized in COMTF newsletter for May 2024.)

Xuechung, K.; Wei, C.; Siliang, L.; Tiejun, W.; Le, Y. & Singh, R. 2024. Spatiotemporal distribution of sudden oak death in the US & Europe. Agricultural & Forest Meteorology. 346: 109891)

Good News!!!! Treatments to Counter Beech Leaf Disease — at least for indidividual trees

beech leaf disease symptoms; photo by Matthew Borden via Flickr

Beech leaf disease (BLD) came to attention in 2012 near Cleveland. It has since spread to the Atlantic – Maine to New Jersey and northern Delaware; south into Virginia; north in Ontario; and west to eastern Michigan.

Scientists have scrambled to understand the disease – how it hijacks the tree’s metabolism; & here its impacts on seedlings, saplings, and mature trees; how it spreads, locations at greatest risk.

(Maryland detections too recent to be shown)

Many of us have despaired.

Now Bartlett Tree Research Laboratories – the research arm of Bartlett Tree Experts – has announced development of Integrated Pest Management (IPM) strategies to treat individual trees – sadly not yet beech in the forest. The project is led by Dr. Andrew Loyd and Dr. Matthew Borden.

Seeing the disease’s impacts on a tree species with aesthetic and ecological values not easily replaced, and its rapid spread, scientists at Bartlett Tree Research Laboratories began testing fungicides and nematicides registered under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) by the U.S. Environmental Protection Agency (EPA) to see whether they might be effective against the causal nematode Litylenchus crenatae ssp mccannii.

As Drs. Loyd and Borden note, managing BLD presents numerous challenges:

1. The disease was discovered recently, so there were many unknowns, including how it spreads and the causal organism’s novel life cycle.

2. The damage occurs in leaf buds during winter dormancy. There has been little previous research on such a system. It is difficult for chemicals to reach the tissues.

3. Mature trees are large, so reaching the vulnerable leaves in the canopy is difficult.

4. Treatment efficacy cannot be evaluated until nearly a year after application.

5. Few chemicals are registered for use against foliar nematodes or for trees in forest, nursery, or landscape settings.

6. Obtaining funding is difficult because protecting beech is a low priority among many of the usual sources.

Fortunately, the leadership at Bartlett – the company’s research department, the New England Division leadership, and especially Robert A. Bartlett, Jr. (head of the family-owned company) – saw the importance of protecting beech and have supported this research. The USDA Forest Service has also funded some of studies exploring soil drenches. Cameron McIntire reports that these studies do not yet have results.

Furthermore, Bartlett has chosen to make the science easily available to all interested parties. Three posters explaining experiments to date are available at ResearchGate. They have also published a study on the early tests of Fuopyram as a foliar spray. It is open-access. Additional publications presenting data on experiments with both spray (Fluopyram) and injection (Thiabendazole/Arbotect) are in preparation.

I summarize briefly here their findings as of August 2024.

In all the trials, the scientists judged efficacy of treatments by counting the number of viable nematodes in leaves, viable nematodes in overwintering buds, and BLD symptom severity at appropriate times before and after treatment (spray or injection).

Tests of foliar sprays on small to medium sized trees

The first tests of foliar applications that resulted in BLD suppression were carried out in Ohio starting in 2021, then expanded to other field sites in Ohio and several states in New England in 2022 and 2023 seasons. In early trials, trees were sprayed four times starting in mid to late July at 21-day intervals. The scientists say that recent trials focus on application timing and rate. They hope that optimizing these factors will help generate new recommendations that are more sustainable while maintaining efficacy.

At the annual meeting of the American Phytopathological Society in July 2023, Bartlett announced that Fluopyram is an effective management tool to combat BLD – on smaller trees that can be treated using foliar application. There are several EPA-registered products, though only one, Broadform, has been so far been granted a section 2(EE) recommendation “For Control of Beech Leaf Disease on Beech Trees.”

Treatments are less effective in situations where the inoculum load is very high (for example, a very dense stand of infected trees); or where mature, untreated canopies hang over treated understory beech.

They suggest that managers focus treatments on high-value specimen beech, collection preservation, and potentially uncrowded mixed natural stands.

Treatments should be made by certified pesticide applicators who are familiar with the disease and treatment specifications. For the injection treatment, technical training and specialized equipment is needed. Bartlett arborists and plant health care specialists in locations affected by BLD have all been trained to perform the treatments, and some other arborists are doing BLD treatments as well using the same products.

Soil drench

Matt Borden said that they tested drenches with three different chemicals. The approach did not reduce nemtatode numbers sufficiently. However, as noted above, the Forest Service is funding additional tests exploring possible combinations of drenches with other actions, such as thinning. Discovering management options across a range of application methods (e.g., foliar, injection, drench) and modes of action is vital for a disease that covers such a broad range of locations and tree sizes and forms.

a macroinjection demonstration; photo by Matthew Borden via Flickr

Injections

Scientists injected Thiabendazole (TBZ) into beech on private land in three locations in Ohio and New Jersey. They tested two application rates and three application timings. They have two years of follow-up data for one site, one year for the others.

Key findings:

nematode numbers in buds in late winter consistently reflected foliar symptoms when the leaves opened.
Injections made before mid-July provided the greatest reduction in nemtatode numbers and best canopy improvement. Trees injected late in the season (30 August), after the nematode has begun dispersing from leaves to buds, exhibited some BLD symptoms the next year, but suffered less canopy dieback than controls.

Margery Daughtrey of Cornell said during a discussion of these finding that the trees’ persistence suggests that trees can tolerate some level of symptoms. Among other things, it might be possible to treat the trees less frequently than annually.

TBZ appears to provide at least two seasons of nematode suppression

Bartlett continues to monitor these trees to see how long the injected chemical suppresses nematode numbers and how long the tree remains healthy. They are also establishing new field sites to further optimize rate and timing.

TBZ – in a product called Arbotect 20-S – has been used to manage Dutch elm disease and sycamore anthracnose since the 1970s. However, it is also a well-known nematicide, previously used as an anti-parasitic drug in human and veterinary medicine. Once injected, TBZ protects the tree for more than one season. The injection technology (MACRO-Injection) has also been used for decades. It infuses the chemical directly into the tree’s vascular system; it does not rely on root uptake. Matt says injection does require take technical skill and the right equipment. To minimize the risk of the wound cracking and weeping, the injection should be done low on the side of the root flare, not on top.

While Arbotect 20-S has been registered for use in 48 states for many years, new labeling is required for its use in beech trees and against BLD. Special Local Needs labels, 24(C)s, have been granted by eight states – Connecticut, Massachusetts, Maine, New Jersey, New York, Pennsylvania, and Virginia. Registration in a ninth – Maryland – is in progress and Bartlett scientists are prepared to apply for several more. The problem is that only a limited number of these “special needs” labels may be issued, and BLD has expanded so far, and so rapidly, that it is already infesting beech in more states than may be covered by 24(C)s. Furthermore, 24(C) labels expire if not renewed. Most current 24(C)s will be active through 2028 – not ideal for a disease that will likely be with us long into the future. The product manufacturer (Syngenta) and distributor (Rainbow Ecoscience) are drafting a change to the main Arbotect 20-S label to add beech and the new nematode pest, but warn that EPA review and approval of amendments can take a very long time. Until then, we must resort to limited special local needs labels, and some states will miss out.

contrasting canopy transparency in beech treated with TBZ v. untreated controls; photo by Matthew Borden

One of the key scientists who developed these treatments for Dutch elm disease, R. Jay Stipes, professor emeritus at Virginia Tech, is quoted by Bartlett rejoicing that his work might help protect another tree species.

Matt believes the treatments will be effective if applied every 2-3 years. This approach would also spread out the cost – which will depend on the arborist but Dave Anderson of Rainbow Ecoscience estimated to be about $25 / inch of dbh.

It is always best to obtain an accurate diagnosis before treatment. The next step is talking through your options with a certified arborist or tree disease specialist. The “good” thing about BLD is that it is a progressive disease and will not kill a tree in a single year. Therefore, waiting until you know the disease is present or active locally is generally recommended.

Tree injection is better than foliar application where the latter is impractical (e.g., the tree is tall) or to reduce runoff, particularly near streams. Bartlett recommends treating any beech larger than 10 cm dbh by injection; smaller trees by foliar spray.

Treated trees should be sound, without serious decay, girdling roots, or other conditions that curtail uptake. Based on research results to date, they recommend treating the tree before mid-July. Bartlett is testing the results of injecting the shortly after full leaf expansion – early to mid-June. Bartlett scientists are testing several application rates to determine how long a single injection will suppress BLD. So far they have had good results from both low and moderate label rates (0.4-1.6 fl oz/inch DBH).

All the technical information re: research into treatments and recommendations for applying either the foliar or injection treatments has been provided by Dr. Matthew Borden of Bartlett Tree Research Laboratories. He can be reached at

mborden@Bartlett.com

https://www.bartlett.com/staff/matthew-borden-dpm

Dr. Borden says he is immensely grateful for the support that allows him and Dr. Loyd to travel widely to establish the BLD research sites and spend weeks collecting data each year with their team. Company founder Francis A. Bartlett established the Bartlett Tree Research Laboratories as a separate entity within the company, where capital is reinvested directly into stable, long-term support of scientific tree research and preservation. The model is well-suited to provide the flexibility and freedom needed to rapidly respond to emerging invasive species issues.

Posted by Faith Campbell

We welcome comments that supplement or correct factual information, suggest new approaches, or promote thoughtful consideration. We post comments that disagree with us — but not those we judge to be not civil or inflammatory.

For a detailed discussion of the policies and practices that have allowed these pests to enter and spread – and that do not promote effective restoration strategies – review the Fading Forests report at https://treeimprovement.tennessee.edu/

www.fadingforests.org

What I learned at the NPB meeting

The National Plant Board’s members are the lead plant health officials of the states and territories. Many federal officials also attend – from APHIS and DHS Bureau of Customs and Border Protection. Representatives of other North American phytosanitary entities participate – i.e., Canada, Mexico, and the North American Plant Protection Organization (NAPPO). Some stakeholder groups participate, especially the nursery industry. I have attended these meetings for over a decade because they provide an overview of pest issues and programs plus an unparalleled opportunity to network. The Nature Conservancy’s Leigh Greenwood also attends. We are the only representatives of the species conservation community to attend – others are missing great opportunities.

Here, I’ve listed 10 items that are among the most important the group discussed.

1) The funding situation for APHIS is worse than I realized

APHIS Administrator Mike Watson and Deputy Administrator (for plants) Mark Davidson both spoke about the need to cut programs to stay within the limits set by congressional appropriations. Funding for APHIS, as a whole, was cut only 1% for the current year (Fiscal Year 2024), cost-of-living salary increases mean less money for programs. (I believe Dr. Watson said $41 million less for FY24). If FY25 funding is the same, Congressionally mandated additional payraises will mean an another $20 million decrease in program funding.

Dr. Davidson said that the plant programs (Plant Protection and Quarantine) had been cut by 5% in FY24. However, Congress did not finalize the funding levels until about half-way through the fiscal year – so staying within the limits required even more severe cuts to programs in the remainder of FY24. To stay within these limits, APHIS cut several programs, among them a $3.6 million cut from the “tree and wood pest” program. This meant loss of funds to manage the polyphagous and Kuroshio shot hole borers, smaller cuts for programs managing Asian longhorned beetle and emerald ash borer, and perhaps the Asian flighted spongy moth. They anticipate additional cuts in these programs in FY25. The one bright light is the Section 7721 Plant Pest & Disease Management & Disaster Prevention Program. It provides steady funding for a range of plant health programs. The House version of the still-pending Farm Bill calls for increasing funding for this program by $15 million each year.

Nearly 100% ash trees in Oregon wetland — exposed to spreading EAB. Photo by Wyatt Williams, Oregon Department of Forestry

Remember this when I ask you to lobby for appropriations! If we don’t advocate for funding the programs dealing with “our” pests, they will shrink.

Watkins and Davidson also worry that whoever is the next secretary of USDA might not support the agency when it seeks to withdraw funds to cover emergencies from the Commodity Credit Corporation – as Secretary Vilsack has.

APHIS and the DHS Customs and Border Protection (CBP) both praised a recent regulatory action that increases user fees for importers having goods cleared at ports. Kevin Harriger, CPB official in charge of agriculture programs, said the new funds would allow CBP to hire 700 new agricultural inspectors (currently there are 2,800 agricultural officials). That sounds great, but … when trade and passenger volumes crashed early in the COVID pandemic, things looked dicey for a while. Plus – as I have argued repeatedly – real protection against pest introductions will come from stronger policies, not ramped-up inspections.

Pathologist Bruce Moltzan reported on the USFS Forest Health Protection program. He pointed out that the USFS has a very limited toolbox. In this fiscal year, the program has about $48 million, after salaries, to support its activities. Projects targetting insects receive 70% of the funding; those targetting pathogens 15%.

2) Invasive hornets

Washington State has not found any new nests of the Northern (formerly Asian) giant hornet (Vespa mandarinia). Miraculous!

However, Georgia detected another species, the yellow-legged hornet (Vespa velutina), near Savannah in August 2023. The Georgia Department of Agriculture, APHIS, and the University of Georgia are working to find nests – which are located at the top of tall pine trees in residential areas. Five nests were found in 2023; another four so far in 2024. Georgia hopes to place traps 100 miles out from each detection site. Like the northern hornet, V. velutina preys on honey bees. It was probably transported by ship or with its cargo.

A third species, V. tropica, has been introduced on Guam.

3) Better Federal-State Cooperation — Sometimes

APHIS and the state phytosanitary officials have set up structures – e.g., Strategic Alliance/Strategic Initiative, or SASI – to work together more closely. CBP joins the coordinating meetings. One program described at the meeting is the effort to contain spread of the box tree moth (Cydalima perspectalis). This effort came out of discussions at last year’s Plant Board meeting, with follow-up gatherings of APHIS, the states, and the nursery industry. The moth is known to be present in New York, Massachusetts, Michigan, Ohio, and now Delaware – plus several Canadian provinces.

A second project concerns how much data to share about state detections of pests – which are recorded in the National Plant diagnostic Network database. These data have accrued over 20 years … and are sought by both other states and academic researchers. States are often reluctant to allow public review of detection data because they fear it will cause other states or private parties to avoid buying plants or other goods from the infested area. While the project team has not yet decided how to deal with these conflicts, they said they were more inclined to share “nonconsequential data” – meaning data on a pest everyone already knows is present, not a pest under regulation or a new detection. In other words, “consequential” seems to pertain to industry profits, not damage to agricultural or natural resources.

EAB-killed ash along Mattawoman Creek, Maryland. Photo by Leslie A. Brice

4) Update: 20 years of tackling the emerald ash borer

Craig Kellogg, APHIS’ chief plant health representative in Michigan, reviewed 20 years of dealing with the emerald ash borer (EAB). He is optimistic about the impact of the biocontrol agents that have now been released in 32 states and four provinces. The larval parasitoids are dispersing and EAB densities are coming down. He conceded that over-story and mature ash are still dying, but says ash in long-infested areas are regenerating well. Scientists agree (see Wilson et al. 2024; full citation at end of the blog). Woodpeckers are still the most effective biocontrol agent of EAB for over-story ash, especially in locations where introduced parasitoids are not established. So far, the growing numbers of biocontrol agents are still parasitizing too few EAB larvae to prevent decline of over-story ash trees.

5) Flighted Spongy Moths

APHIS reported on recent detections of flighted spongy moth from Asia on ships coming to U.S. ports. The program covers four closely related species of Lymantria. All have much broader host ranges than Lymantria dispar, plus the females are capable of sustained flight, so they spread more rapidly.

The principal strategy to prevent their introduction is to require ships that call at ports along the Pacific coast in Russia, China, Japan, and North and South Korea to ensure that the ships’ superstructures and cargo are clean. Before arriving at U.S. ports, the ship’s captain must inform CBP where it has called over the last 24 months. Then, CBP conducts an inspection. If CBP inspectors find a small number of egg masses, they remove the eggs and spray pesticide. If the inspectors detect a large number of egg masses, the ship is ordered to leave port, clean itself, and undergo re-inspection before it can return.

Four countries in the Americas – the U.S., Canada, Chile, and Argentina – and also New Zealand have very similar programs.

Detections follow natural changes in population levels in the exporting regions. APHIS’ program leader, Ingrid Asmundsson, reported on an unfortunate coincidence in 2014. A huge moth population outbreak occurred simultaneously with very low fuel prices in Russia. The latter attracted many ships to call there. An even bigger population surge occurred in 2019. Asmundsson expects another high-moth period this year.

flighted spongy moths infesting a ship superstructure

APHIS is working on putting this program on a regulatory foundation; this would allow the agency to be more specific in its requirements and to impose penalties (other than expulsions from ports). I’ll let you know when the proposed rule is published for comment.

6) Regional Reports: Old Pests, New Pests

Representatives of the regional plant boards informed us of their “new pest” or other concerns.

Gary Fish, president of the Eastern Plant Board, mentioned

the need for additional research on management of beech leaf disease
concern about impact of box tree moth and vascular streak dieback on the nursery industry (the latter is a threat to dogwood and redbud)
spread of elm zig-zag sawfly in Vermont and Connecticut
awareness that laurel wilt is moving into Virginia and maybe farther north.

elm zig-zag sawfly; photo by Gyorgy Csoka *via* Bugwood

There was a more general discussion of beech leaf disease. What can be done, given that the disease is so widespread that no one is regulating movement of beech. Gary Fish advised outreach and efforts to reach agreement on management approaches. Chris Benemann, of Oregon, suggested informing other states so that they can decide whether to take regulatory action. A representative of CBP urged engaging stakeholders by asking for their help.

Chris Benemann, President of the Western Plant Board, expressed concern about APHIS’ reduced funding for spongy moth detection and control efforts. She also worries about the recently detected population of Phytophthora austrocedrii in an Oregon nursery. The western states are also focused on several longstanding pest problems – grasshoppers, Japanese beetle; and a new beetle from Australia that is attacking almonds, pistachios, and walnuts.

tree infested by hemlock woolly adelgid; photo by F.T. Campbell

Megan Abraham of Indiana reported that members of the Central Plant Board are concerned about

funding decrease for APHIS and USFS efforts to slow the spread of spongy moth and manage Asian longhorned beetle and emerald ash borer;
Invaders associated with Christmas decorations, e.g., hemlock woolly adelgid, elongate hemlock scale, and balsam woolly adelgid
spotted lanternfly finding new ways to travel;
invasion by beech leaf disease and possibly by sudden oak death;
elm zig-zag sawfly entering the region;
boxwood blight, potato pests, honeybee pests, and invasive plants – e.g., Hydrilla.

She noted that nursery stock is increasingly coming from more distant – and cheaper – producers, raising the risk of new pests being introduced.

Finally, Abraham expressed concern about decreased funding at the same time as the need is growing – and asked with whom states should collaborate in order to reverse this trend.

Kenny Naylor of Oklahoma, Vice President of the Southern Plant Board, concurred that funding levels are a major concern. He mentioned specifically the spongy moth Slow the Spread program and eradication of the Asian longhorned beetle outbreak in South Carolina. Another concern is the Georgia hornet outbreak.

7) Phasing Out Post-Entry Quarantine

APHIS and the NPB have agreed to phase out the post-entry quarantine (PEQ) program. A program review revealed several problems, some of which astound me. When examining plants in quarantine the scientists still relying on visual inspection! And they are looking for pests identified 45 years ago (1980)! While I think PEQ programs can be valuable in preventing introduction of disease agents, as implemented in recent decades it does not. Twenty years ago, citrus longhorned beetles escaped from a “quarantine” area in a commercial nursery in Washington state. These Cerambycids are more than an inch long!

citrus longhorned beetle; photo by Art Wagner, USDA *via* Bugwood

Part of this phase-out is to transfer plant species harboring pests of concern to the Not Authorized for Importation Pending Pest Risk Assessment (NAPPRA). While the APHIS speaker said that NAPPRA allows the agency to act quickly when it detects evidence of pest risk, I have found lengthy delays. The third round of proposals was published in December 2019! The fourth round of species proposed for NAPPRA listing should be published soon; a fifth round is now in draft inside the agency.

8) Christmas Greens – Spreading Pests

Officials from Oregon, Maine, and Illinois described their concerns about pests being spread by shipments of various forest or plant products, especially Christmas greens. Mentioned were spongy moths, link hemlock woolly adelgid, link elongate hemlock scale, balsam woolly adelgid, link and box wood moth. Part of the challenge is that the vectoring items are often sold by unregulated outlets – multiple stores, Christmas tree lots – and through on-line or catalog outlets. There are also extreme demands on the regulatory enforcement staff during the brief holiday sales season. Several states are unsure whether they have authority over decorative products – although others pointed out that they are regulating the pest, regardless of the object for sale or type of store.

9) Pests in Firewood

Leigh Greenwood of The Nature Conservancy noted that the state agencies that issue firewood regulations – often the plant protection organization (state department of agriculture) — do a good job alerting the public about the risks and rules. However, the public looks first to state parks agencies for information about camping – and those agencies have less robust educational efforts. It is important to put the message where the public can find it when they don’t know it exists – before they include firewood from home in their camping gear.

10) Projects of the North American Plant Protection Organization

The North American Plant Protection Organization (NAPPO) is working on several projects of interest to those of us concerned about tree-killing pests. One project is evaluating risks associated with wood products, especially how well one international regulation, ISPM#15 is working for dunnage. Another projects is testing the efficacy of the heat treatment specified by ISPM#15 (50^o C for 30 minutes). A third project — almost completed – is evaluating fumigants that can be alternatives to methyl bromide.

In conclusion, each annual meeting of the National Plant Board is packed with new information, updates on current pests, and comments on by the state agencies who suggest new approached to APHIS and hold the agency to account. It is well worth attending. Information about upcoming meetings of both the national and four regional plant boards is posted on the NPB website, https://www.nationalplantboard.org/

Signatories to the APHIS-NPB strategic alliance

SOURCE

Wilson, C.J., T.R. Petrice, T.M. Poland, and D.G. McCullough. 2024. Tree species richness and ash density have variable effects on emerald ash borer biological control by woodpeckers & parasitoid wasps in post-invasion white ash stands. Environmental Entomology.

Posted by Faith Campbell

www.fadingforests.org

APHIS Annual Report Describes Helpful Programs … Since Cut Back Because of Funding Shortfalls

Flighted spongy moths infesting a ship’s superstructure

USDA’s Animal and Plant Health Inspection Service (APHIS) has issued its annual report for Fiscal Year 2023. The report is part of an enhanced outreach effort that I believe is an effort to persuade the Congress to provide additional funds. However, as I describe below, at this summer’s annual meeting of the National Plant Board, link APHIS’ leadership stated that funding shortfalls are forcing them to curtail many programs. These include ones important to those of us concerned about threats to North American trees. I applaud this action and hope it succeeds!

The report contains some good news but I consider the overall approach depressing. Tree-killing pests continue to receive little attention. The report also emphasizes APHIS’ efforts to facilitate export of agricultural products – an understandable stance given American politics.

The opening summarizes the agency’s activities includes:

Examples of programs targetting pests abroad, before they can reach the U.S. All are fresh fruits and vegetables;
APHIS or staff at U.S. borders:
- Approved (cleared) 27,235 shipmentscontaining over 1.87 billion plant units (e.g., a single plant or cutting, or vial of tissue culture plantlets) and 670,811 kilograms of seeds. They intercepted 2,176 quarantine pests. (APHIS carry out these inspections at Plant Inspection Stations – separate from the port environment where DHS Customs and Border Protection (CBP) staff inspects other cargo.)

Identified approximately 92,000 pestsfound during CBP inspections of cargo, mail, and express carrier shipments and took quick action to prevent those of concern from entering the U.S.
Facilitated entry of regulated agricultural cargo by monitoring more than 62,000 treatments of various kinds, that is, fumigations, cold or heat treatments, and irradiation.
Examples of APHIS’ efforts to slow pests’ spread within the country cited plant pest surveys — with coordinated responses — for approximately 45 pests. Also APHIS described funding to help citrus growers combat citrus greening.
The report has separate subreports on the following programs: risk analysis, pest detection, “specialty crop” pests, and tree and wood pests. The last two contain information specific to our interests.

Tree and Wood Pests

This program protects forests, private working lands, and natural resources. It targets specific pests: the Asian longhorned beetle, emerald ash borer, spongy moth, and most recently the invasive shot hole borers. The report notes that numerous native, widespread hardwood tree species are vulnerable to these pests. APHIS asserts an economic justification for the program: conserving forests enhances rural communities’ economic vitality, supports forest-related industries, and maintains the ecosystem services provided by urban trees.

Unfortunately, at this summer’s annual meeting of the National Plant Board APHIS leadership said funding shortfalls forced them to pull back on all these programs.

Programs as Described in the Report

Asian Longhorned Beetle

ALB eradication aims to protect the 30% of U.S. trees that are ALB hosts. These trees support multi-billion-dollar maple syrup, timber, tree nursery, trade, and tourism industries. After reviewing the history of ALB detections, starting in Brooklyn in August 1996, the report describes APHIS’ eradication strategy as comprising surveys, regulatory inspections and quarantine restrictions, removal of infested and high-risk trees, and chemical treatment applications. In FY 2023, the program surveyed more than 763,000 trees across the four regulated areas: New York, Massachusetts, Ohio, and South Carolina. Each program is summarized.

Good news at two locations. On Long Island: only 11 new infested trees were found after a survey of 43,480 trees. In Worcester County, Massachusetts, no new infested trees were found after surveying nearly 360,000 trees. However, in Tate Township, Ohio, surveys detected 163 new infested trees. And in

South Carolina, the program is at an earlier stage — surveying a portion of the quarantine area. The program surveyed nearly 140,000 trees and removed 1,700 in FY 2023.

At the National Plant Board Meeting, Deputy Administrator Mark Davidson explained that the FY2024 appropriation cut $3.6 million from the “tree and wood pests” account. This required the agency to reduce funding for the ALB eradication program.

Emerald Ash Borer

The report summarizes the spread of EAB since its first detection in 2002 in Michigan to 37 states and the District of Columbia (APHIS does not mention EAB’s presence in five Canadian provinces.)

Saying that EAB has spread beyond what a regulatory program can control, the report notes that APHIS ended the regulatory program in FY 2021. In FY 2023 the agency continued the transition to a program relying primarily on biocontrol. In FY2023, APHIS provided parasitoids to 155 release sites – three in Canada, the rest in 122 counties in 25 states. APHIS and cooperators continue to assess their impacts on EAB populations and tree health at release sites and nearby areas. Field evaluations indicate the EAB parasitoid wasps and other EAB natural enemies (woodpeckers) are protecting regenerating sapling ash from EAB.

Spongy Moths

Spongy moths (the species formerly called European gypsy moths) are established in all or parts of 20 eastern and midwestern states, plus the District of Columbia. APHIS and state cooperators regulate activities in the quarantine area to prevent the moths’ human-assisted spread to non-quarantine (non-infested) areas – primarily West coast states. To address the moths’ natural spread, APHIS PPQ monitors the 1,200-mile-long border of the quarantine area and adds newly infested areas to the regulated area. The USDA Forest Service – APHIS – Slow-the-Spread Foundation program has greatly reduced the moth’s rate of spread and has eradicated isolated populations.

Another component of the program aims to prevent introduction of members of the flighted spongy moth complex link from Asia. The Asian species have broader host ranges and the females can fly, so they could spread faster. A multi-nation cooperative program is designed to prevent the moths’ hitchhike on vessels coming from Asia. link APHIS supports this program through negotiations and support of CBP’s offshore vessel inspection, certification, and cleaning requirements. Canada participates in the same program.

In FY 2023, APHIS and state cooperators continued efforts to delimit possibly introductions in Washington State (no additional moths detected); and California and Oregon (initial detections in FY 2020).

California sycamore infested by polyphagous shot hole borer; photo by Beatriz Nobua-Behrmann UC Cooperative Extension

Shot Hole Borers

The report notes that various non-native shot hole borers have been detected in several states. Their hosts include trees in forests and urban landscapes, tea plantations, and avocado orchards. The program’s focus was apparently on the polyphagous and Kuroshio shot hole borers devastating riparian habitats in southern California and urban areas in other parts of California. At California’s request, APHIS and the USDA Forest Service helped establish a working group, led by USFS, with the goal of strategically addressing both shot hole borers in California. In FY 2023, APHIS’ helped with foreign explorations for possible biocontrol agents, as well as host specificity testing.

APHIS leadership told the National Plant Board in July 2024 that it had dropped this entire program due to funding shortfalls.

Specialty Crop Pests

While much of this report concerns pests of agricultural crops (e.g., grapes, citrus, potatoes), it also summarized efforts re: Phytophthora ramorum (sudden oak death) and spotted lanternfly. APHIS says its efforts protected nursery stock production worth approximately $1.3 billion as of 2019, and tree fruit production worth approximately $1.7 billion in 2021.

map showing areas of the Eastern United States at risk to *P. ramorum* – developed by Gilligan of Cambridge University

Phytophthora ramorum

The report states that APHIS seeks to limit P. ramorum’s spread from affected nurseries. The agency does this via regulatory strategies. During FY 2023, 16 nurseries were governed by more stringent rules under the federal program which are imposed on nurseries that have been determined in past years to harbor P. ramorum-infected plants.

In addition, Oregon officials continued surveys of an area outside its quarantine zone because of a detection the previous year. APHIS will adjust the federal quarantine depending on the state’s findings.

The APHIS report does not discuss several pertinent events that occurred in FY2023. [For more details, read the California Oak Mortality Task Force newsletters for 2023 – posted here.

First, APHIS does not mention or discuss the implications of detection of two new strains of P. ramorum — EU1 & NA2 — in west coast forests. The presence of EU1 in a new California county (Del Norte) was confirmed in Feb 2023.

Second, the report said that Oregon is trying to determine the extent of the P. ramorum infection detected outside the state’s quarantine zone. However, it does not mention that this outbreak involves the new NA2 lineage – and that NA2 was known to be present in nurseries in the region since 2005.

The report also does not clarify that three nurseries to added to the more stringent program were so treated because SOD-infected plants were found on their premises.

Nor does the report note that at least two new naturally-infected hosts of P. ramorum were identified: Western sword fern (Polystichum munitum) and Arbutus x ‘Marina’.Koch’s postulates need to be completed on the latter so it has not yet been added to APHIS’ official host list.

Spotted Lanternfly

Spotted Lanternfly (SLF) was found in 16 states in FY 2023. APHIS’ program enjoyed funding provided through Specialty Crop Pests and from the Plant Protection Act’s Section 7721 link ($6 million from the latter).

The report notes that APHIS still does not have enough data to determine SLF’s impacts on agriculture. Thus far, vineyards have been the most adversely affected agricultural segment, mostly due to SLF acting as a stressor to vines. Also, the sticky, sugary “honeydew” produced by SLF attracts other insects and promotes sooty mold growth. These can ruin the fruit and further damage the plant.

SLF populations are strongly linked to major transportation pathways, such as railroads and interstate highways. APHIS targets treatments and, in some areas, removes SLF’s preferred host plant (tree of heaven [Ailanthus]), from transportation hubs. The aim is to reduce the risk of SLF’ spread to new areas and to eradicate isolated infestations. In FY 2023, APHIS and cooperators treated 4,637 properties covering 6,455 acres in affected areas. However, during the National Plant Board meeting both state and APHIS officials complained to me that managers of these transportation hubs raise many barriers to their access, sharply limiting the program’s chance of success.

*Ailanthus altissima* – drive of spotted lanternfly invasion

The program was expanded after National Environmental Policy Act-mandated environmental review. This allowed APHIS to conduct treatments in four additional states—Indiana, Massachusetts, Michigan, and Rhode Island. In addition, program cooperators identified three potential biological control organisms, one that targets the tree of heaven and two that target SLF. APHIS will continue to evaluate them and develop methods to rear them in the laboratory.

Finally, in fiscal year 2023, APHIS joined the National Association of State Departments of Agriculture and the National Plant Board to develop a national strategic plan outlining the future direction of the SLF program. With the strategic plan, PPQ aims to harmonize the approach across states to slow SLF’s spread, develop consistent outreach messaging for a nationwide audience, and more effectively use existing state and Federal resources. Continued spread of SLF despite the huge effort, rising costs of the program, and new scientific findings spurred reconsideration of the strategy.

To summarize, I hope that APHIS’ annual report will – in the future – help members of Congress and their staff understand the agency’s programs’ purpose and past successes. This increased understanding might make it easier to advocate for more funding. I am troubled, however, by the agency’s glossing over significant problems.

Posted by Faith Campbell

www.fadingforests.org

Two new Phytophthora arrivals (plus another looming) in U.S. forests & nurseries

Breeding Port-Orford cedar for resistance to Phytophthora lateralis; photo by Richard Sniezko, USDA Forest Service

At the annual meeting of the National Plant Board in July, I learned that two new Phytophthora species have been detected in the United States. Questions remain about how each arrived.

Phytophthora austrocedrii

This species was detected in a nursery in Oregon, then traced back to a supplier in Ohio. Officials are trying to determine how it entered the country – and then spread.

junipers in Great Britain killed by *P. austrocedri*; Forestry Research

In the United Kingdom, P. austrocedri has killed trees in the Juniperus and Cupressus genera. Damage is particularly significant at two sites in northern Scotland and in England’s Lake District. The principal host, Juniperus communis, is an important native species. It is already considered vulnerable. P. austrocedri has also been detected in Argentina, where it is killing the native Chilean or Patagonian cedar (Austrocedrus chilendris). The cedar species is the only one in the genus. Evidence indicates the pathogen was introduced to both Britain and Argentina; but its origin is unknown. Indeed, the species was first isolated by scientists as an unknown Phytopthora taxon on a juniper in an import/export nursery in Germany. All reported hosts are members of the Cupressaceae family (UK forest research website).

Of greater concern to Americans, P. austrocedri has also infected individual trees of Port-Orford cedar (Chamaecyparis lawsoniana). (UK forest research website).

Port-Orford cedar is a species endemic to a small range in southwestern Oregon and Northwestern California.

POC populations have been severely reduced over the past century by a different non-native Phytophthora, P. lawsonii. US Forest Service scientists recently announced that they have bred trees resistant to this pathogen – and offered seedlings for widespread planting.

Possible hosts in the Pacific Northwest – other than Port Orford cedar – include Juniperus californica, Juniperus grandis, Juniperus occidentalis, and Juniperus maritima – although the junipers might be limited to arid environments, where they would presumably be less vulnerable. https://plants.usda.gov/home/classification/15147

Research in Great Britain shows that P. austrocedri spreads in water and by movement of infected plants and contaminated soil. Footwear, camping equipment, and vehicle tires can all carry the pathogen. This makes the pathogen particularly difficult to control (this is another similarity with P. lawsonii).

Phytophthora abietivora

P. abietivora was originally found on a diseased Christmas tree (Fraser fir, Abies fraseri) in Connecticut in 2019. It has since been reported in Pennsylvania and Virginia; and in forest nurseries and Christmas tree plantations in Quebec and Ontario. The Canadians report that it has not caused disease (Canadian website). However, the Canadian representative at the National Plant Board meeting expressed concern and asked USDA APHIS to clarify what actions it is taking regarding this species.

(Natural populations of Fraser fir have been severely reduced over the past century by the balsam woolly adelgid.)

Fraser fir killed by balsam woolly adelgid; Clingman’s Dome, Great Smoky Mountains National Park

Several additional hosts have been identified, including balsam fir (Abies balsamea) and eastern hemlock (Tsuga canadensis); and deciduous or hardwood species: hickory (Carya sp.), flowering dogwood (Cornus florida), American witch hazel (Hamamelis virginiana), mountain holly (Ilex montana), red maple (Acer rubrum), silver birch (Betula lenta), American beech (Fagus grandifolia); and several oaks: white (Quercus alba), chestnut (Q. montana) and northern red oak (Q. rubra) (Canadian fact sheet).

According to the Canadian website, P. abietivora causes root rot and subsequent foliar chlorosis, discoloration, stem cankers, and sometimes tree decline and death. Determining which Phytophthora species is the causal agent of a tree’s symptoms requires laboratory testing. The Canadian fact sheet reports that wet, cool conditions provide ideal environments for P. abietivora. Like other Phytophthora species, P. abietivora can be spread through soil and water, as well as via infected plant material or pots or trays (particularly if soil remains on the equipment). The Canadian fact sheet has several photographs illustrating symptoms and additional sources.

Liriodendron tulipifera; photo by Evelyn Simak via Geograph

Phytophthora kernoviae

P. kernoviae was first detected in southwestern England in 2003. link In England, this pathogen has caused significant diseases in native Fagus sylvatica (European beech) and lesions on trunks of a European oak, Quercus robur. More worrying are the trunk lesions on the North American native yellow or tulip poplar (Liriodendron tulipifera) and lesions on foliage of Monterey pine (Pinus radiate), giant sequoia(Sequoiadendron giganteum), and several North American native shrubs, Rhododendron macrophyllum (Pacific rhododendron), R. occidentale (western rhododendron), R. catawbiense (Catawba rosebay) and Umbellularia californica (California bay laurel).

*Phytophthora kernoviae* on *R. ponticum* in Cornwall

The infestation in Cornwall is sustained by heavy sporulation on the non-native shrub Rhododendron ponticum, which is invasive in woodlands. Worrying for Americans is the fact that P. kernoviae sporulates on three plant species native to West coast forests — Rhododendron macrophyllum, R. occidentale, and Umbellularia californica – as well as on R. catawbiense, which is native to the southern Appalachians.

USDA APHIS requested adoption of a “response plan” targetting P. kernoviae under the National Plant Disease Recovery System (NPDRS). This plan was adopted in 2008 and updated in 2015.

The recovery plans found the areas at highest risk are eastern slopes of the Appalachian Mountains because this area combines a native sporulating host and residential landscaping choices that are likely to include hosts that could transport the pathogen. A lower risk was identified for West Coast forests.

Because of this status, P. kernoviae is also a “priority” pest for surveys under the Cooperative Agricultural Pest Survey (CAPS) program. According to Purdue University’s “pest tracker” website four states have reported carrying out surveys for P. kernoviae in one or more years since 2016: Oregon, Tennessee, Pennsylvania, and Virginia. Surveys in Oregon were carried out in 2018 – 2020. In 2020 the counties surveyed included Curry County, where three strains of P. ramorum link have become established. The Purdue list is not certified as accurate or complete. To date, no surveys have detected P. kernoviae in the United States or – I believe – in Canada.

SOURCES

Canadian fact sheet at https://inspection.canada.ca/en/plant-health/invasive-species/plant-diseases/p-abietivora/fact-sheet; accessed July 2024

Canadian website at https://inspection.canada.ca/en/plant-health/invasive-species/plant-diseases/p-abietivora accessed July 2024

Purdue University’s “pest tracker” website at pesttracker.org. Survey Status of Phytophthora leaf blight – Phytophthora kernoviae . (2023) accessed July 2024

UK research website at https://www.forestresearch.gov.uk/tools-and-resources/fthr/pest-and-disease-resources/phytophthora-austrocedri-disease-of-juniper-and-cypress/ accessed July 2024

For details on existence of two clonal lineages of Phytophthora austrocedrii, see Henricot, B. A. Perez-Sierra, A.C. Armstrong, P.M. Sharp, and S. Green. Phytopathology 2017. 107:12, 1532-1540.

Posted by Faith Campbell